Cardiovascular autonomic neuropathy is typically caused by metabolic, toxic and/or genetic damage to autonomic nerve fibers, and/or by metabolic, toxic and/or genetic damage to small diameter nerve fibers. Cardiovascular autonomic neuropathy is common, for example, in individuals with diabetes. Prevalence estimates vary, but it is probable that at least 25% of the diabetes population suffers from cardiovascular autonomic neuropathy.
There are many clinical manifestations of cardiovascular autonomic neuropathy including, but not limited to, resting tachycardia, exercise intolerance and orthostatic hypotension.
Cardiovascular autonomic neuropathy is often associated with silent myocardial ischemia (i.e., a “silent heart attack”), and is also associated with high rates of sudden death.
Additionally, with cardiovascular autonomic neuropathy, damage to nerves in the cardiovascular system can interfere with the body's ability to adjust blood pressure and heart rate. As a result, blood pressure may drop sharply after sitting or standing, causing a person to feel light-headed or even to faint. Damage to the nerves that control heart rate can mean that the heart rate stays high, instead of rising and falling in response to normal body functions and exercise. All of these effects can be detrimental to the patient's health.
There are several standard medical tests which are performed to help diagnose cardiovascular autonomic neuropathy. These tests generally require that the patient perform different specific physical exercises while the patient's electrocardiogram (ECG) is monitored. In particular, changes in the patient's heart rate (from one beat to the next) are traditionally observed before, during and after the test, depending on the specific test being performed. More specifically, the time interval between the peaks in two sequential “R” waves in the ECG waveform—sometimes called the “R-R” interval, and also commonly known as beat-to-beat “heart rate variability” (HRV)—is monitored and analyzed.
The most common tests performed to diagnose cardiovascular autonomic neuropathy are as follow:                1. Testing HRV In Response To Metronomic Or Paced Breathing At 6 Times Per Minute (“Metronomic Breathing Tests”). With the patient at rest and supine, the patient breathes at a rate of 6 breaths/minute while the heart rate is monitored by an ECG device. A difference in heart rate between inspiration and expiration of >15 beats/minute is considered normal, and a difference in heart rate between inspiration and expiration of <10 beats/minute is considered abnormal.        2. Testing HRV In Response To The Valsalva Maneuver (“Valsalva Manuever Tests”). The patient forcibly exhales into a mouthpiece while an associated manometer measures pressure. The patient exhales hard enough to increase the exhalation pressure to approximately 40 mm Hg for 15 seconds while the ECG is monitored. Often this test is conducted in a simpler manner, by simply having the patient attempt to exhale through the mouth while the mouth is closed so as to create a high backpressure condition, but this closed-mouth approach is generally not preferred since it tends to suffer from inconsistent repeatability. Healthy patients develop tachycardia during strain, and an overshoot bradycardia upon release. The ratio of longest R-R to shortest R-R should generally be >1.2 in healthy patients.        3. Testing HRV In Response To Standing (“HRV Standing Tests”). During continuous ECG monitoring, the patient's R-R interval is measured at beats 15 and 30 after standing. Normally, a tachycardia is followed by reflex bradycardia (i.e., an abnormally slow heartbeat, usually less than 60 beats per minute). The 30:15 ratio is normally >1.03 in healthy patients.        
Many systems are available to perform cardiovascular autonomic neuropathy testing. However, most of these systems are essentially just conventional ECG machines adapted for simple HRV analysis. More particularly, with these systems, the skin of the patient is prepared for the application of 3 or more individual ECG electrodes. These electrodes are generally applied to the shoulders and/or chest of the patient, and possibly to one or both legs of the patient, thus requiring that the patient at least partially disrobe. The ECG electrodes are then connected with wires to the system's ECG monitor.
Detection of the patient's breathing is generally conducted using a permanent, and relatively expensive, airflow pressure transducer, to which a disposable mouthpiece is attached. While generally effective, this arrangement constitutes a relatively expensive solution to the problem of monitoring metronomic breathing. The use of a permanent airflow pressure transducer also raises the possibility of cross-contamination by infectious agents, since the transducer is reused from patient to patient.
The Ansar ANS-R1000 system (The Ansar Group, Inc. of Philadelphia, Pa.) is one such cardiovascular autonomic neuropathic testing product that is currently commercially available. The Anscore Health Management System (Boston Medical Technologies, Inc. of Wakefield, Mass.) was another (the company is no longer in business). However, the Ansar ANS-R1000 system and the Anscore Health Management System are/were complex systems, requiring highly trained operators and requiring significant preparation of the patient due to the need to apply the ECG electrodes to the patient (and the associated patient disrobing). These systems, and others like them, are not believed to constitute a readily-available, cost-effective and/or practical in-office, rapid-diagnostic tool for application to the primary care physician and/or small clinic markets.
The complexity, inconvenience, and required time and expense associated with currently-available cardiovascular autonomic neuropathic testing systems all act to inhibit wider adoption of these systems. This is a serious issue in view of, for example, the rapidly growing incidence of Type 1 and Type 2 diabetes, which makes this type of testing increasingly important for diagnosing the cardiovascular autonomic neuropathy linked to these types of diabetes.
Thus, a disposable, multi-purpose cardiovascular autonomic neuropathy testing device would be a key enabling component in a new, low-cost, small form-factor, battery-powered, dedicated cardiovascular autonomic neuropathy testing system.
It is, therefore, a principal object of the present invention to provide a disposable, multi-purpose testing device which can be used to quickly and easily test for cardiovascular autonomic neuropathy.